Chapter 3 Telescopes 2017 Pearson Education Inc Units of Chapter 3 Optical Telescopes Telescope Size HighResolution Astronomy Radio Astronomy SpaceBased Astronomy Summary of Chapter 3 ID: 636846
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Chapter 3 Telescopes
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Units of Chapter 3
Optical Telescopes
Telescope SizeHigh-Resolution Astronomy
Radio Astronomy
Space-Based Astronomy
Summary of Chapter 3
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3.1 Optical Telescopes
Images can be
formed through
reflection or
refraction.
Reflecting mirror
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3.1 Optical Telescopes
Refracting lens
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3.1 Optical Telescopes
Image
formation
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3.1 Optical Telescopes
Reflecting and refracting telescopes
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3.1 Optical Telescopes
Modern telescopes are all reflectors:
Light traveling through lens is refracted differently depending on wavelength.Some light traveling through lens is absorbed.
A large lens can be very heavy and can only be supported at the edge.
A lens needs two optically acceptable surfaces, but a mirror needs
only
one.
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3.1 Optical Telescopes
Types of reflecting telescopes
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3.1 Optical Telescopes
Details of the Keck telescope
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3.1 Optical Telescopes
Image acquisition
: Charge-coupled devices (CCDs) are electronic devices that can be quickly read out and reset.
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3.1 Optical Telescopes
Image processing by computers can sharpen images.
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Discovery 3.1: The
Hubble Space Telescope
The
Hubble Space Telescope
has several instruments.
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Discovery 3.1: The
Hubble Space Telescope
Resolution achievable by the
Hubble Space Telescope
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3.2 Telescope Size
Light-gathering
power
: Improves
our ability to see
the faintest
parts of this galaxy
Brightness is proportional to
square
of radius of mirror
The figure, part (b) was
taken with
a telescope twice the size
of
(a).
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3.2 Telescope Size
Multiple telescopes: Mauna Kea
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3.2 Telescope Size
The VLT (Very Large Telescope), Atacama, Chile
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3.2 Telescope Size
Resolving power
: When better, can distinguish objects that are closer together.
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3.2 Telescope Size
Resolution is proportional to wavelength and inversely proportional to telescope size.
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3.2 Telescope Size
Effect of improving resolution:
(a) 10
′
; (b) 1
′
; (c) 5
″
; (d) 1
″
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3.3 High-Resolution Astronomy
Atmospheric blurring due to air movements
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3.3 High-Resolution Astronomy
Solutions:
Put telescopes on mountaintops, especially in deserts.Put telescopes in space.
Use active optics—control mirrors by bending them slightly to correct for atmospheric distortion.
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3.4 Radio Astronomy
Radio telescopes
:Similar to optical reflecting telescopesPrime focus
Less sensitive to imperfections (due to longer wavelength); can be made very large
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3.4 Radio Astronomy
Largest radio telescope: 300-m dish at Arecibo
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Longer wavelength means poorer angular resolution.
Advantages of radio astronomy:
Can observe 24 hours a day.Clouds, rain, and snow don’t interfere.
Observations at an
entirely different
frequency get totally
different information.
3.4 Radio Astronomy
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3.4 Radio Astronomy
Interferometry
:
Combines
information from
several
widely separated radio telescopes
as if it
came from
a single dish.
Resolution will be
that of
a dish
whose diameter
=
largest separation between dishes
.
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3.4 Radio Astronomy
Interferometry requires preserving the phase relationship between waves over the distance between individual telescopes.
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3.4 Radio Astronomy
These telescopes can
get radio images whose resolution is
close to
optical.
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3.4 Radio Astronomy
Interferometry can also be done with visible light, but it is much harder due to shorter wavelengths.
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3.5 Space-Based Astronomies
Infrared radiation can image where visible radiation is blocked by interstellar matter or atmospheric particles.
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3.5 Space-Based Astronomies
Infrared telescopes can also be in space or flown on balloons.
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3.5 Space-Based Astronomies
Ultraviolet images
The Cygnus loop supernova remnant
M81
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3.5 Space-Based Astronomies
X-rays and gamma rays will not reflect off mirrors as other wavelengths do; need new techniques.
X-rays will reflect at a very shallow angle and can therefore be focused.
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3.5 Space-Based Astronomies
X-ray image of supernova remnant Cassiopeia A
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3.5 Space-Based Astronomies
Gamma rays are the most high-energy radiation we can detect. This supernova remnant would be nearly invisible without the Fermi satellite and its gamma-ray detector.
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3.5 Space-Based Astronomies
Much can be learned from
observing the
same astronomical object at many
wavelengths
. Here, the Milky Way.
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Summary of Chapter 3
Refracting telescopes make images with a lens.
Reflecting telescopes make images with a mirror.Modern research telescopes are all reflectors.
CCDs are used for data collection.
Data can be formed into images, analyzed
spectroscopically
, or used to measure intensity.
Large telescopes gather much more light, allowing study of very faint sources.
Large telescopes also have better resolution.
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Summary of Chapter 3, cont.
Resolution of ground-based optical telescopes is limited by atmospheric effects.
Resolution of radio or space-based telescopes is limited by diffraction.Active and adaptive optics can minimize atmospheric effects.
Radio telescopes need large collection area; diffraction is limited.
Interferometry can greatly improve resolution.
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Summary of Chapter 3, cont.
Infrared and ultraviolet telescopes are similar to optical.
Ultraviolet telescopes must be above the atmosphere.
X-rays can be focused, but very differently from visible light.
Gamma rays can be detected. This must be done from space.
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